CN112088332A

CN112088332A - Holographic waveguides including birefringence control and methods for their manufacture

Info

Publication number: CN112088332A
Application number: CN201980029130.9A
Authority: CN
Inventors: J·D·沃德恩; M·M·波波维奇; A·J·格兰特
Original assignee: DigiLens Inc
Current assignee: DigiLens Inc
Priority date: 2018-03-16
Filing date: 2019-03-18
Publication date: 2020-12-15
Also published as: WO2019178614A1; JP2021515917A; JP7487109B2; EP4372451A2; US11726261B2; EP3765897A4; US11150408B2; US10690851B2; EP3765897A1; KR20200133265A; EP3765897B1; US20200319404A1; US20190285796A1; US20220137294A1

Abstract

Many embodiments according to the present invention are directed to waveguides that implement birefringence control. In some embodiments, the waveguide includes a birefringent grating layer and a birefringent control layer. In a further embodiment, the birefringence control layer is compact and efficient. Such structures may be used in a variety of applications, including but not limited to: compensating for polarization dependent losses in the holographic waveguide; providing a three-dimensional LC director arrangement in a Bragg grating based waveguide; and spatially varying the angular/spectral bandwidth for homogenizing the output from the waveguide. In some embodiments, polarization-preserving, wide-angle, and highly reflective waveguide cladding with polarization compensation is achieved for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing quarter-wave or half-wave retardation.

Description

Holographic waveguides including birefringence control and methods for their manufacture

Technical Field

The present disclosure relates to optical waveguides, and more particularly, to waveguide displays using birefringent gratings.

Background

A waveguide may be referred to as a structure having the ability to confine and guide a wave (i.e., limit the spatial region in which the wave may propagate). One sub-category comprises optical waveguides as structures that can guide electromagnetic waves, typically in the visible spectrum. Waveguide structures can be designed to control the propagation path of a wave using a number of different mechanisms. For example, planar waveguides may be designed to utilize diffraction gratings to diffract and couple incident light into the waveguide structure such that the coupled-in (in-coupled) light may continue to travel within the planar structure via total internal reflection ("TIR").

Fabrication of the waveguide may include the use of a material system that allows the holographic optical element to be recorded within the waveguide. One class of such materials includes polymer dispersed liquid crystal ("PDLC") mixtures, which are mixtures comprising photopolymerizable monomers and liquid crystals. Other subclasses of such mixtures include holographic polymer dispersed liquid crystal ("HPDLC") mixtures. Holographic optical elements, such as volume phase gratings, can be recorded in such liquid mixtures by irradiating the material with two mutually coherent laser beams. During the recording process, the monomers polymerize and the mixture undergoes a photo-polymerization induced phase separation, resulting in areas densely packed with liquid crystal droplets interspersed with transparent polymer areas. The alternating liquid crystal-rich and liquid crystal-poor regions form the fringe planes of the grating.

Waveguide optics such as those described above may be considered for a range of display and sensor applications. In many applications, waveguides containing one or more grating layers encoding a variety of optical functions can be implemented using various waveguide architectures and material systems, enabling new innovations in near-eye displays for augmented reality ("AR") and virtual reality ("VR"), compact heads-up displays ("HUDs") for air and land transportation, and sensors for biometric and LIDAR ("LIDAR") applications.

Disclosure of Invention

Below, a more detailed description of various concepts of the inventive optical display and method for displaying information and embodiments thereof follows. It should be appreciated that the various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes. A more complete understanding of the present invention may be derived by considering the following detailed description in conjunction with the accompanying drawings, in which like reference numbers refer to similar components. For the purpose of clarity, details relating to technical material that is known in the technical fields related to the invention have not been described in detail.

One embodiment includes a waveguide comprising: at least one waveguide substrate, at least one birefringent grating; at least one birefringent control layer, a light source for outputting light, an input coupler for directing the light into a total internal reflection path within the waveguide, and an output coupler for extracting light from the waveguide, wherein interaction of the light with the birefringent control layer and the birefringent grating provides a predefined characteristic of the light extracted from the waveguide.

In another embodiment, the interaction of the light with the birefringence control layer provides at least one of: an angular or spectral bandwidth change, a polarization rotation, a birefringence change, an angular or spectral dependence of at least one of beam transmission or polarization rotation, and a light transmission change in at least one direction in the plane of the waveguide substrate.

In a further embodiment, the predefined characteristic varies across the waveguide.

In a further embodiment, the predefined characteristic is due to a cumulative effect of the interaction of the light with the birefringence control layer and the birefringence grating along at least one light propagation direction within the waveguide.

In yet a further embodiment, the predefined characteristic comprises at least one of: uniform illumination and uniform polarization over the angular range of the light.

In a further embodiment, the birefringence control layer provides compensation for polarization rotation introduced by the birefringent grating along at least one direction of light propagation within the waveguide.

In yet a further embodiment, the birefringence controlling layer is a liquid crystal and polymer material system.

In another additional embodiment, the birefringence control layer is a liquid crystal and polymer system aligned using directional ultraviolet radiation.

In further additional embodiments, the birefringence control layer is aligned by at least one of: electromagnetic radiation, electric or magnetic fields, mechanical forces, chemical reactions, and thermal exposure.

In yet another embodiment, the birefringence control layer affects the alignment of the LC director in a birefringent grating formed in a liquid crystal and polymer system.

In still further embodiments, the birefringence control layer has an anisotropic refractive index.

In yet another embodiment, the birefringence control layer is formed on at least one of the inner optical surface or the outer optical surface of the waveguide.

In yet a further embodiment, the birefringence control layer comprises at least one stack of refractive index layers disposed on at least one optical surface of the waveguide, wherein at least one of the stack of refractive index layers has an isotropic refractive index and at least one of the stack of refractive index layers has an anisotropic refractive index.

In yet another additional embodiment, the birefringence control layer provides a highly reflective layer.

In yet further additional embodiments, the birefringence control layer provides optical power.

In yet another embodiment, the birefringence control layer provides an environmental isolation layer for the waveguide.

In yet a further embodiment, the birefringence control layer has a gradient index structure.

In yet another additional embodiment, the birefringence control layer is formed by stretching a layer of optical material to spatially change its refractive index in the plane of the waveguide substrate.

In yet further additional embodiments, the light source provides collimated light in angular space.

In yet another embodiment, at least one of the input coupler and the output coupler comprises a birefringent grating.

In yet a further embodiment, the birefringent grating is recorded in a material system comprising at least one polymer and at least one liquid crystal.

In yet another additional embodiment, the at least one birefringent grating comprises at least one birefringent grating for providing at least one of the following functions: beam expansion in a first direction, beam expansion in a second direction and extraction of light from the waveguide, and coupling of light from a source into a total internal reflection path in the waveguide.

In yet a further additional embodiment, the light source comprises a laser and the alignment of the LC director in the birefringent grating is spatially varied to compensate for the illumination stripe.

Yet another additional embodiment includes a method of manufacturing a waveguide, the method comprising providing a first transparent substrate, depositing a layer of grating recording material, exposing the layer of grating recording material to form a grating layer, forming a birefringence control layer, and applying a second transparent substrate.

In yet still further additional embodiments, the grating recording material layer is deposited onto the substrate, the birefringence control layer is formed on the grating layer, and the second transparent substrate is applied over the birefringence control layer.

In yet another additional embodiment, the grating recording material layer is deposited onto the substrate, the second transparent substrate is applied over the grating layer, and the birefringence control layer is formed on the second transparent substrate.

In yet still further additional embodiments, the birefringence control layer is formed on the first transparent substrate, the grating recording material layer is deposited on the birefringence control layer, and the second transparent substrate is applied over the grating layer.

In yet a further embodiment, the method further comprises depositing a layer of liquid crystal polymer material, and aligning the liquid crystal polymer material using oriented UV light, wherein the layer of grating recording material is deposited onto the substrate, and the second transparent substrate is applied over the aligned liquid crystal polymer layer.

In yet still another additional embodiment, the layer of liquid crystal polymer material is deposited onto one of the grating layer or the second transparent substrate.

In yet another additional embodiment, the layer of liquid crystal polymer material is deposited onto the first transparent substrate, the layer of grating recording material is deposited onto the aligned liquid crystal polymer material, and the second transparent substrate is applied over the grating layer.

Additional embodiments and features are set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the specification or may be learned by practice of the invention. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings which form a part of this disclosure.

Drawings

These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying data and drawings, in which:

figure 1 conceptually illustrates a schematic cross-sectional view of a waveguide including a birefringent grating and a birefringent control layer, in accordance with an embodiment of the present invention.

Figure 2 conceptually illustrates a schematic cross-sectional view of a waveguide including a birefringent control layer and a birefringent grating for compensating for the birefringence of the grating, according to some embodiments of the present invention.

Figure 3 conceptually illustrates a schematic cross-sectional view of a waveguide including a birefringent control layer and a birefringent grating for providing uniform output illumination from the waveguide, in accordance with an embodiment of the present invention.

Fig. 4 conceptually illustrates a schematic cross-sectional view of a birefringence control layer formed by combining a multilayer structure of an isotropic refractive index layer and an anisotropic refractive index layer according to an embodiment of the present invention.

Fig. 5 conceptually illustrates a schematic cross-sectional view of a birefringent control layer formed by combining a multilayer structure of an isotropic refractive index layer and an anisotropic refractive index layer integrated with a birefringent grating layer, according to an embodiment of the present invention.

FIG. 6 conceptually illustrates a plan view of a dual expansion waveguide having a birefringent control layer, in accordance with an embodiment of the present invention.

Figure 7 conceptually illustrates a schematic cross-sectional view of a waveguide including a birefringence control layer and a birefringence grating for correcting birefringence introduced due to an optical element in the output light path from the waveguide, in accordance with an embodiment of the present invention.

FIG. 8 conceptually illustrates a schematic plan view of an apparatus for aligning a birefringent control layer by applying a force to an edge of the layer, in accordance with an embodiment of the present invention.

Fig. 9A-9F conceptually illustrate process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringent control layer, according to various embodiments of the present invention.

10A-10F conceptually illustrate process steps and apparatus for fabricating a waveguide including a birefringence control layer and a birefringent grating applied to an outer surface of the waveguide, in accordance with various embodiments of the present invention.

11A-11F conceptually illustrate process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringent control layer, according to various embodiments of the present invention.

FIG. 12 conceptually illustrates a flow chart showing a method of manufacturing a waveguide including a birefringent grating and a birefringent control layer, in accordance with an embodiment of the present invention.

FIG. 13 conceptually illustrates a flow chart showing a method of manufacturing a waveguide including a birefringence control layer and a birefringence grating applied to an outer surface of the waveguide, in accordance with an embodiment of the present invention.

Figure 14 conceptually illustrates a flow diagram showing a method of manufacturing a waveguide including a birefringent grating and a birefringent control layer, in which forming the birefringent control layer is performed before recording the grating layer, according to an embodiment of the present invention.

Figure 15 conceptually illustrates a schematic side view of a waveguide having a birefringence control layer applied at the waveguide-to-air interface, in accordance with an embodiment of the present invention.

Figure 16 conceptually illustrates a schematic side view of a waveguide having a birefringent control layer applied to the waveguide-to-air interface that isolates the waveguide from its environment, in accordance with an embodiment of the present invention.

Figure 17 conceptually illustrates a schematic side view of an apparatus for manufacturing a structure comprising a birefringent grating layer overlaid on a birefringent control layer, with a grating recording beam propagating through the birefringent control layer, according to an embodiment of the present invention.

FIG. 18 conceptually illustrates a schematic side view of an apparatus for manufacturing a structure including a birefringent control layer overlying a birefringent grating layer, where the birefringent control layer is aligned by UV radiation propagating through the grating, according to an embodiment of the invention.

Figure 19 conceptually illustrates a cross-section of a waveguide comprising substrates sandwiching a grating layer.

Figure 20 conceptually illustrates a waveguide with an inserted quarter wave polarizing layer, according to an embodiment of the present invention.

Figure 21 conceptually illustrates a schematic cross-sectional view showing a portion of a waveguide illustrating the use of a quarter wave polarizing layer with an RKV grating, according to an embodiment of the invention.

Figure 22 conceptually illustrates a polarizing layer architecture comprising LCP quarter wave cells and Reactive Monomer Liquid Crystal Mixture (RMLCM) cells separated by an index matching oil layer, according to an embodiment of the invention.

Figure 23 conceptually illustrates an example of a polarizing architecture based on grating elements having a layer of RMLCM grating material in direct contact with a bare LCP film, according to an embodiment of the present invention.

Figure 24 conceptually illustrates a cross-sectional view schematically showing an example of a polarization layer architecture in which a bare LCP layer is bonded to a bare RMLCM layer, in accordance with an embodiment of the present invention.

Fig. 25 conceptually illustrates a cross-sectional view schematically showing an example of a polarization layer architecture using an RMLCM layer as a polarization layer, according to an embodiment of the present invention.

Figure 26 conceptually illustrates an example of a polarization layer architecture that includes features for compensating for polarization rotation introduced by a birefringent grating, in accordance with an embodiment of the present invention.

Figure 27 conceptually illustrates a plan view of a waveguide display that schematically shows features that incorporate the embodiment of figure 26, in accordance with an embodiment of the present invention.

Fig. 28 and 29 conceptually illustrate cross-sectional views schematically showing examples of polarizer layer architectures comprising an upper substrate, an LCP layer with a hard encapsulating layer, an RMLCM layer, and a lower substrate, in accordance with various embodiments of the present invention.

Figure 30 conceptually illustrates a plan view that schematically shows a first example of a two-region polymer film, in accordance with an embodiment of the present invention.

Figure 31 conceptually illustrates a plan view that schematically shows a second example of a two-region polymer film, in accordance with an embodiment of the present invention.

Figure 32 conceptually illustrates a plan view that schematically shows a third example of a two-region polymer film, in accordance with an embodiment of the present invention.

Figure 33 conceptually illustrates a diagram showing a transparent aperture layout, in accordance with an embodiment of the present invention.

Figure 34 conceptually illustrates a plan view that schematically shows a waveguide that includes an output grating, a turning grating, and an input grating that include K vectors and an alignment layer fast axis direction for each grating, in accordance with an embodiment of the present invention.

Detailed Description

For the purposes of describing the embodiments, some well-known features of optical technology known to those skilled in the art of optical design and visual displays have been omitted or simplified in order not to obscure the underlying principles of the invention. Unless otherwise stated, the term "on-axis" with respect to the direction of a light ray or beam refers to propagation parallel to an axis perpendicular to the surface of an optical component described with respect to the present invention. In the following description, the terms light, ray, beam and direction may be used interchangeably and are associated with each other to indicate the direction of propagation of electromagnetic radiation along a straight track. The terms light and illumination may be used with respect to the visible and infrared bands of the electromagnetic spectrum. Portions of the following description will be presented using terminology commonly employed by those skilled in the art of optical design. In the following description, the term grating may be used to indicate any kind of diffractive structure used in a waveguide, including holograms and Bragg (Bragg) or volume holograms. The term grating may also cover gratings comprising groups of gratings. For example, in some embodiments, the input grating and the output grating each comprise two or more gratings multiplexed in a single layer. For purposes of illustration, it is understood that the drawings are not to scale unless otherwise indicated.

Referring generally to the drawings, systems and methods relating to waveguide applications incorporating birefringence control according to various embodiments of the present invention are illustrated. Birefringence is the optical property of a material having a refractive index that depends on the polarization and the direction of propagation of light. A birefringent grating may be referred to as a grating having such properties. In many cases, birefringent gratings are formed in liquid crystal polymer material systems such as, but not limited to, HPDLC blends. The polarization characteristics of such a grating may depend on the average relative permittivity and the relative permittivity modulation tensor.

Many embodiments according to the present invention are directed to waveguides that implement birefringence control. In some embodiments, the waveguide includes a birefringent grating layer and a birefringent control layer. In a further embodiment, the birefringence control layer is compact and efficient. Such structures may be used in a variety of applications, including but not limited to: compensating for polarization dependent losses in the holographic waveguide; providing a three-dimensional LC director arrangement in a Bragg grating based waveguide; and spatially varying the angular/spectral bandwidth for homogenizing the output from the waveguide. In some embodiments, polarization-preserving, wide-angle, and highly reflective waveguide cladding with polarization compensation is achieved for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing quarter-wave or half-wave retardation. In various embodiments, a polarization-maintaining, wide-angle birefringence control layer is implemented for modifying the polarization output of a waveguide to balance the birefringence of an external optical element used with the waveguide.

In many embodiments, the waveguide includes at least one input grating and at least one output grating. In further embodiments, the waveguide may include additional gratings for various purposes, such as, but not limited to, a turning grating for beam expansion. The input grating and the output grating may each comprise a multiplexed grating. In some embodiments, the input grating and the output grating may each comprise two overlapping grating layers that are in contact or vertically separated by one or more thin optical substrates. In some embodiments, the grating layer is sandwiched between glass or plastic substrates. In some embodiments, two or more such grating layers may form a stack within which total internal reflection occurs at an external substrate and air interface. In some embodiments, the waveguide may include only one grating layer. In some embodiments, electrodes may be applied to the face of the substrate to switch the grating between the diffractive state and the transparent state. The stack may also include additional layers such as a beam splitting coating and an environmental protection layer. The input grating and the output grating shown in the figures may be provided by any of the grating configurations described above. Advantageously, the input grating and the output grating may be designed to have a common surface grating pitch. In the case where the waveguide also contains grating(s) other than the input and output gratings, the gratings may be designed to have grating pitches such that the vector sum of the grating vectors is substantially zero. The input gratings may combine gratings oriented such that each grating diffracts a polarization of incident unpolarized light into the waveguide path. The output gratings may be configured in a similar manner such that light from the waveguide paths is combined and coupled out of the waveguide as unpolarized light. Each grating features at least one grating vector (or K-vector) in 3D space, which in the case of a bragg grating is defined as the vector perpendicular to the bragg fringes. The grating vector may determine the optical efficiency for a given range of input and diffraction angles. In some embodiments, the waveguide comprises at least one surface topography grating. Waveguide grating structures, material systems, and birefringence control are discussed in further detail below.

Switchable Bragg grating

The optical structures recorded in the waveguide may include many different types of optical elements such as, but not limited to, diffraction gratings. In many embodiments, the grating implemented is a bragg grating (also referred to as a volume grating). The bragg grating may have a high efficiency with little light being diffracted into higher orders. The relative amounts of light in the diffracted and zeroth orders can be varied by controlling the refractive index modulation of the grating, a characteristic of which can be used to make a lossy waveguide grating for extracting light in a large pupil. One type of grating used in holographic waveguide devices is a switchable bragg grating ("SBG"). SBGs can be made by first placing a thin film of a mixture of photopolymerizable monomers and liquid crystal material between glass plates or substrates. In many cases, the glass sheets are in a parallel configuration. One or both glass plates may support electrodes (typically transparent tin oxide films) for applying an electric field across the film. The grating structure in SBG can be recorded in a liquid material, commonly referred to as a syrup (syrup), by photo-polymerization induced phase separation using interferometric exposure with spatially periodic intensity modulation. Factors such as, but not limited to, controlling the radiation intensity, the volume fraction of the components of the material in the mixture, and the exposure temperature can determine the resulting grating morphology and performance. As can be readily appreciated, a wide variety of materials and mixtures may be used depending on the specific requirements of a given application. In many embodiments, HPDLC materials are used. During the recording process, the monomers polymerize and the mixture undergoes phase separation. The LC molecules aggregate to form discrete or coalesced droplets that are periodically distributed in the polymer network on the scale of the optical wavelength. The alternating liquid crystal-rich and liquid crystal-poor regions form the fringe planes of the grating, which can produce bragg diffraction with a strong optical polarization due to the alignment ordering of the LC molecules in the droplet.

The resulting volume phase grating can exhibit very high diffraction efficiency, which can be controlled by the magnitude of the electric field applied across the membrane. When an electric field is applied to the grating via the transparent electrode, the natural orientation of the LC droplets may change, causing the refractive index modulation of the fringes to decrease and the holographic diffraction efficiency to drop to a very low level. Typically, the electrodes are configured such that the applied electric field will be perpendicular to the substrate. In many embodiments, the electrodes are fabricated from indium tin oxide ("ITO"). In the OFF state with no electric field applied, the extraordinary axis (extraordinary axis) of the liquid crystal is aligned substantially perpendicular to the stripes. The grating thus exhibits high refractive index modulation and high diffraction efficiency for P-polarized light. When an electric field is applied to the HPDLC, the grating switches to an ON state in which the extraordinary axis of the liquid crystal molecules is aligned parallel to the applied electric field and thus perpendicular to the substrate. In the ON state, the grating exhibits lower refractive index modulation and lower diffraction efficiency for both S-polarized light and P-polarized light. And thus the grating regions no longer diffract light. Depending on the function of the HPDLC device, each grating region may be divided into a plurality of grating elements, such as, for example, a matrix of pixels. Typically, the electrodes on one substrate surface are uniform and continuous, while the electrodes on the opposite substrate surface are patterned according to a plurality of selectively switchable grating elements.

One of the known attributes of transmissive SBGs is that the LC molecules tend to align with an average direction perpendicular to the plane of the grating fringes (i.e., parallel to the grating or K vector). The effect of the LC molecular alignment is that the transmitting SBG efficiently diffracts P-polarized light (i.e., light having a polarization vector in the plane of incidence), but has a diffraction efficiency of almost zero for S-polarized light (i.e., light having a polarization vector perpendicular to the plane of incidence). As a result, when the angle between incident and reflected light is small, the transmissive SBG cannot generally be used at near grazing incidence because the diffraction efficiency of any grating for P-polarization drops to zero. Furthermore, in holographic displays that are sensitive to only one polarization, illumination light with an unmatched polarization is not efficiently trapped.

HPDLC material system

HPDLC mixtures according to various embodiments of the invention generally include LC, monomers, photoinitiator dyes, and coinitiators. The mixture (often referred to as a slurry) often also includes a surfactant. For the purposes of describing the present invention, a surfactant is defined as any chemical agent that reduces the surface tension of the total liquid mixture. The use of surfactants in HPDLC mixtures is known and dates back to the earliest studies on HPDLC. For example, the papers SPIE, vol 2689, 158-169, 1996, to r.l. sutherland et al, the disclosure of which is incorporated herein by reference, describe PDLC mixtures comprising monomers, photoinitiators, co-initiators, chain extenders and LC to which surfactants can be added. Surfactants are also mentioned in the Journal of Nonlinear Optical Physics and Materials, volume 5, No. I89-98, 1996, of Natarajan et al, the disclosure of which is incorporated herein by reference. Furthermore, U.S. patent No.7,018,563 to Sutherland et al discusses a polymer dispersed liquid crystal material for forming a polymer dispersed liquid crystal optical element, the polymer dispersed liquid crystal material comprising: at least one acrylic monomer; at least one type of liquid crystal material; a photoinitiator dye; a co-initiator, and a surfactant. The disclosure of U.S. patent No.7,018,563 is incorporated herein by reference in its entirety.

The patent and scientific literature contains many examples of material systems and processes that can be used to fabricate SBGs, including research into formulating such material systems for achieving high diffraction efficiencies, fast response times, low drive voltages, and the like. Both U.S. patent No.5,942,157 to Sutherland and U.S. patent No.5,751,452 to Tanaka et al describe combinations of monomers and liquid crystal materials suitable for fabrication of SBG devices. Examples of formulations can also be found in papers dating back to the early 90 s of the 20 th century, many of these materials used acrylate monomers, including:

r.l. sutherland et al, chem.mater, 5, 1533(1993), describes the use of acrylate polymers and surfactants, the disclosure of which is incorporated herein by reference. Specifically, the formulation includes a cross-linked multifunctional acrylate monomer; chain extender N-vinyl pyrrolidone, LC E7, photoinitiator rose bengal and co-initiator N-phenylglycine. In some variants the surfactant octanoic acid is added.

Fontechio et al SID 00Digest 774-.

Y.h.cho et al, Polymer International, 48, 1085-.

Karasawa et al, Japanese Journal of Applied Physics, Vol.36, 6388-.

Multifunctional acrylate monomers are also described by T.J.Bunning et al, Polymer Science: Part B: Polymer Physics, Vol.35, 2825-2833, 1997, the disclosure of which is incorporated herein by reference.

Lanacchiene et al, Europhysics Letters, Vol 36(6), 425-430, 1996, describe PDLC mixtures comprising pentaacrylate monomers, LC, chain extenders, co-initiators and photoinitiators, the disclosure of which is incorporated herein by reference.

Acrylates offer the advantages of fast kinetics, good mixing with other materials, and compatibility with film forming processes. Since acrylates are crosslinked, they tend to be mechanically robust and flexible. For example, functional 2(di) and 3(tri) urethane acrylates have been widely used in HPDLC technology. Higher functionality materials such as penta and hexa functional dry (penta and hex functional) materials have also been used.

Overview of Birefringence

Holographic waveguides based on HPDLC offer the benefits of switching capability and high refractive index modulation, but suffer from intrinsic birefringence due to the alignment of the liquid crystal director along the grating vector during the LC polymer phase separation. While this may result in a large degree of polarization selectivity, which may be advantageous in many applications, adverse effects such as polarization rotation may occur in gratings designed to perform turning and expansion of a waveguide beam in the waveguide plane (known as turning gratings). This polarization rotation can result in efficiency losses and output light non-uniformity.

Two common methods for modifying the alignment of the LC director include the application of alignment layers and rubbing. Generally, by such means, the LC director in a plane parallel to the alignment layer can be realigned within that plane. In HPDLC bragg gratings, this problem is made more challenging by the natural alignment of the LC director along the grating K vector, making all but the simplest grating alignment a complex three-dimensional problem and rendering conventional techniques using rubbed or polyamide alignment layers impractical. Other methods may include the application of electric fields, magnetic fields, and mechanical pressure during curing. These methods have shown limited success when applied to reflective gratings. However, such techniques are generally not easily convertible to a transmissive bragg grating waveguide.

The main design challenge in waveguides is to couple image content from an external projector into the waveguide efficiently and in such a way that the waveguide image is free of dispersion and brightness non-uniformity. The use of a laser may be implemented in order to overcome chromatic dispersion and achieve reasonably good collimation. However, lasers can suffer from pupil banding artifacts (pupil banding artifacts) that manifest themselves as output illumination non-uniformities. When replicating (expanding) a collimated pupil in a TIR waveguide, banding artifacts can be created. Basically, each time a light beam interacts with a grating, the light beams diffracted out of the waveguide may have a gap or overlap, resulting in an illumination ripple. In many cases, waviness varies with field angle, waveguide thickness, and aperture thickness. The banding may be smoothed by the chromatic dispersion typically exhibited by broadband sources such as LEDs. However, LED illumination is not completely free of banding problems, and in addition, this tends to result in bulky input optics and increased waveguide thickness. De-banding is minimized using pupil shifting techniques to configure the light coupled into the waveguide such that the input grating has an efficient input aperture that varies with the TIR angle. Techniques for performing pupil shifting are described in international application No. pct/US2018/015553, entitled "motion Device with Uniform Output Illumination," the disclosure of which is incorporated herein by reference in its entirety.

In some cases, the polarization rotation that occurs in the turning grating (described above) may compensate for the illumination stripes in the waveguide that are illuminated with the laser. The mechanism is that the large number of grating interactions in the turning grating combined with the small polarization rotation of each interaction can average out the strips (due to imperfect matching of the TIR beam and other related optical effects such as, but not limited to, parasitic gratings left from the recording process, stray light interaction with the grating and waveguide surfaces, etc.). The process of birefringence compensation can be aided by fine tuning the spatial variation of birefringence (alignment of the LC director) in the turning grating.

A further problem that arises in waveguide displays is that contact with moisture or surface combinations can frustrate waveguide Total Internal Reflection (TIR), resulting in image gaps. In such cases, the extent of use of the protective outer layer may be limited by the need for low index materials that will provide TIR within the waveguide angular bandwidth. A further design challenge in waveguides is to maintain high efficiency over the angular bandwidth of the waveguide. An exemplary solution would be a polarization-maintaining, wide-angle, and highly reflective waveguide cladding. In some applications, polarization balancing within the waveguide may be achieved using a quarter-wave retardation layer or a half-wave retardation layer applied to one or both of the major reflective surfaces of the waveguide. However, in some cases, a practical retarder film may add an unacceptable thickness to the waveguide. Thin film coating of the desired formulation will typically require an expensive and time consuming vacuum coating step. One exemplary method of achieving a coating includes, but is not limited to, using inkjet printing or an industry standard spin coating process. In many embodiments, the coating may be applied directly to the printed grating layer. Alternatively, a coating may be applied to the outer optical surface of the assembled waveguide.

In some applications, the waveguide is used in combination with conventional optics to correct aberrations. Such aberrations are caused when the waveguide is used in applications such as, but not limited to, automotive HUDs that project images onto an automotive windshield for reflection into the eye-ward range of an observer. The curvature of the windshield can introduce significant geometric aberrations. Since many waveguides operate with collimated beams, it can be difficult to pre-compensate for distortions within the waveguide itself. One solution includes mounting a pre-compensation optical element near the output surface of the waveguide. In many cases, the optical element is molded from plastic and may introduce severe birefringence that should be balanced by the waveguide.

In view of the above, many embodiments of the present invention are directed to a birefringence control layer designed to address one or more of the problems set forth above. For example, in many embodiments, a compact and efficient birefringence control layer is implemented for compensating polarization-dependent losses in a holographic waveguide, for providing a three-dimensional LC director arrangement in a bragg grating-based waveguide, for spatially varying the angular/spectral bandwidth to homogenize the output from the waveguide, and/or for isolating the waveguide from its environment while ensuring confinement of the waveguide beam. In some embodiments, polarization-maintaining, wide-angle, and highly reflective waveguide cladding with polarization compensation is implemented for grating birefringence. In several embodiments, a thin polarization control layer is implemented for providing quarter-wave or half-wave retardation. The polarization control layer may be implemented as a thin layer directly on top of the grating layer, or into one or both of the waveguide substrates using standard spin-on or inkjet printing processes. In various embodiments, a polarization-maintaining, wide-angle birefringence control layer is implemented for changing the polarization output of a waveguide to balance the birefringence of an external optical element used with the waveguide. Other implementations and specific configurations will be discussed in further detail below.

Waveguide applications including birefringence control

Waveguides and waveguide displays implementing birefringence control techniques according to various embodiments of the present invention may be implemented using a number of different techniques. In some embodiments, the waveguide includes a birefringent grating layer and a birefringent control layer. In a further embodiment, a compact and efficient birefringent control layer is realized. The birefringent control layer may be implemented for various functions, such as, but not limited to: compensating for polarization dependent losses in the holographic waveguide; providing a three-dimensional LC director arrangement in a Bragg grating based waveguide; and efficient and cost-effective integration within the waveguide for spatially varying the angular/spectral bandwidth for homogenizing the output from the waveguide. In any of the embodiments to be described, the birefringence control layer may be formed on any optical surface of the waveguide. For purposes of understanding the present invention, the optical surface of the waveguide may be one of a TIR surface, a surface of a grating layer, a surface of a waveguide substrate sandwiching the grating layer, or a surface of any other optical substrate implemented within the waveguide (e.g., a beam splitter layer for improved uniformity).

FIG. 1 conceptually illustrates a waveguide implementing a birefringent control layer, according to an embodiment of the present invention. In the illustrated embodiment, the waveguide apparatus 100 includes an optical substrate 101, the optical substrate 101 including a birefringent grating layer 102 and a birefringent control layer 103. As shown, light 104 propagating under TIR within the waveguide interacts with the two layers. For example, a light ray 104A having an initial polarization state indicated by symbol 104B, after propagating through the grating region around point 102A, has its polarization rotated to state 104C. The birefringent control layer 103 rotates the polarization vector to state 104D, which state 104D is the polarization state used to achieve some predefined diffraction efficiency for light ray 104E when light ray 104E interacts with the grating around point 102B and diffracts into direction 104F with polarization state 104G, which is similar to state 104D. As will be shown in the following description, many different configurations of birefringent control layers and birefringent gratings may be implemented according to various embodiments of the present invention.

Figure 2 conceptually illustrates a waveguide device 200, the waveguide device 200 including at least one optical substrate 201 and a coupler 202 for deflecting light 203A, 203B (over a range of incident angles) from an external source 204 into

TIR paths

205A, 205B in the waveguide substrate. Light in the TIR path may interact with an output grating, which may be configured to extract a portion of the light each time the TIR light satisfies a grating diffraction condition. In the case of bragg gratings, extraction may occur when the bragg condition is satisfied. More precisely, efficient extraction can occur when the light incident on the grating is within the angular and spectral bandwidth around the bragg condition. These bandwidths are defined in terms of some measure of acceptable diffraction efficiency, such as but not limited to 50% of the peak DE. For example, light in

TIR ray paths

205A, 205B is diffracted by the output grating into

output directions

206A, 206B, 207A, and 207B at different points along the output grating. It should be clear from the basic geometrical optics that a unique TIR angle can be defined by each light incidence angle at the input grating.

Many different types of optical elements may be used as couplers. For example, in some embodiments, the coupler is a grating. In several embodiments, the coupler is a birefringent grating. In many embodiments, the coupler is a prism. The device further comprises at least one birefringent grating 208 for providing beam expansion in a first direction and light extraction from the waveguide and at least one birefringent control layer 209 having anisotropic refractive index characteristics. In the embodiment to be discussed, the source 204 may be an input image generator comprising a light source, a micro display panel and optics for collimating light. As can be readily appreciated, a variety of input image generators may be used, including input image generators that output non-collimated light. In many embodiments, the input image generator projects an image for display on the microdisplay panel such that each display pixel is converted into a unique angular orientation within the substrate waveguide. The collimating optics may include lenses and mirrors, which may be diffractive lenses and mirrors. In some embodiments, the source may be configured to provide illumination that is not modulated with image information. In several embodiments, the light source may be a laser or an LED, and may include one or more lenses for varying the angular characteristics of the illumination beam. In various embodiments, the image source may be a microdisplay or an image scanner.

For any direction of light, the interaction of the light with the birefringent control layer 209 and the birefringent grating 208 integrated along the total internal reflection path may provide predefined characteristics of the light extracted from the waveguide. In some embodiments, the predefined characteristic includes at least one of a uniform polarization or a uniform illumination over a range of angles of light. Fig. 2 also illustrates how the birefringent control layer 209 and the grating 208 provide uniform polarization. In many embodiments, the input state will correspond to P-polarization, which can be used for the grating recorded in the HPDLC. For purposes of explaining the present invention, an initial polarization state is assumed, indicated at 210. The interaction of light near the grating interaction region along TIR path 205A with the birefringent control layer is represented by polarization states 211, 212, the polarization states 211, 212 showing the rotation of the polarization vector before and after propagating through the thickness AB of the birefringent control layer 209. This polarization rotation may be designed to balance the polarization rotation of the thickness CD of the adjacent grating regions encountered by the light ray along TIR path 205A. Thus, the polarization of the light extracted by the grating may be aligned parallel to the input polarization vector, as indicated by polarization state 213. In some embodiments, the output polarization state may be different from the input polarization state. In many embodiments, such as the embodiment shown in fig. 2, the birefringent grating at least partially overlaps the birefringent control layer. In several embodiments, the two are separated by a portion of the waveguide path.

FIG. 3 conceptually illustrates a waveguide device 300 in which a birefringent control layer and a grating provide uniform output illumination, according to an embodiment of the present invention. In the illustrated embodiment, the waveguide apparatus 300 includes at least one optical substrate 301 and a coupler 302, the coupler 302 for deflecting light 303 from an external source 304 into a TIR path 305 in the waveguide substrate. The device 300 further comprises at least one birefringent grating 306 for providing beam expansion in a first direction and light extraction from the waveguide and at least one birefringent control layer 307 having anisotropic refractive index characteristics. As shown, light in the TIR ray path 305 may be diffracted by the output grating into

output directions

308, 309. For the purpose of explaining the present invention, assume a relationship of initial beam illumination (I) and angle (U) distribution, indicated at 310. The interaction of light near the grating interaction region along the TIR path 305 with the birefringent control layer 307 is characterized by an illumination distribution before (311) and an illumination distribution after (312) propagating through the thickness AB of the birefringent control layer. In some applications, such as but not limited to display applications, the waveguide apparatus 300 may be designed to have uniform, angular illumination across the exit pupil of the waveguide. This may be achieved by matching the angular birefringence characteristics of the birefringent control layer to the angular bandwidth of the grating (along the grating path CD in the vicinity of the approach path AB) such that light (indicated by 308, 309) extracted by the grating integrated on the waveguide exit pupil provides uniform illumination with respect to the angular distribution 313. In some embodiments, the characteristics of the grating and the birefringence control layer vary over the aperture of the waveguide.

Implementing birefringent control layers

The birefringence control layer may be provided using a variety of materials and manufacturing processes. In many embodiments, the birefringent control layer has anisotropic refractive index characteristics that can be controlled during fabrication to provide a spatial distribution of birefringence such that for any direction of light, the interaction of the light with the birefringent control layer and birefringent grating integrated along the total internal reflection path provides a predefined characteristic of the light extracted from the waveguide. In some embodiments, the layer may be implemented as a thin stack comprising more than one layer.

Depending on the grating configuration, the arrangement of HPDLC gratings can present significant challenges. In the simplest case of a planar grating, the polarization control may be constrained to a single plane orthogonal to the plane of the grating. A scrolling K-vector raster may require a change in alignment across the raster plane. A turning grating, particularly one with tilted bragg fringes, can have a much more complex birefringence, requiring a 3D arrangement, and in some cases a much higher spatially resolved arrangement.

The following examples of birefringent control layers used with the present invention are illustrative only. In each case, it is assumed that the layer is processed such that properties are changed across the surface of the layer. It is further assumed that the birefringent control layer is arranged within the waveguide containing the grating or on an optical surface of the waveguide. In some embodiments, the birefringent control layer is in contact with the grating layer. In several cases, the birefringence control layer is split into separate parts and disposed on different surfaces of the waveguide. In various embodiments, the birefringent layer may comprise a plurality of layers.

In some embodiments, the present invention provides a thin polarization control layer that can provide quarter-wave or half-wave retardation. The polarization control layer may be implemented as one or both of a thin layer directly on top of the grating layer or into the waveguide substrate using standard spin-coating or inkjet printing processes.

In one set of embodiments, the birefringence control layer is formed using a material that can utilize a polymer network and liquid crystals that are 3D aligned using directed UV light. In some embodiments, the birefringence control layer is formed at least in part from a Liquid Crystal Polymer (LCP) network. The LCP, also referred to in the literature as a reactive polyarylate, is a polymerizable liquid crystal comprising liquid crystalline monomers including, for example, reactive acylated termini that polymerize with each other in the presence of a photoinitiator and directed UV light to form a rigid network. The mutual polymerization of the ends of the liquid crystal molecules can freeze their orientation into a three-dimensional pattern. The process typically involves coating a material system comprising a liquid crystal polymer on a substrate and prior to annealing, selectively aligning the LC directors using an orientation/spatially controllable UV source. In some embodiments, the birefringent control layer is at least partially formed from a photoalignment layer, which is also referred to in the literature as a Linear Polymeric Photopolymer (LPP). The LPP may be configured to align the LC director parallel or perpendicular to the incident linearly polarized UV light. The LPP can be formed as a very thin layer (typically 50nm) to minimize the risk of scattering or other parasitic optical effects. In some embodiments, the birefringence control layer is formed of LCP, LPP and at least one dopant. The LC directors can be aligned in the complex three-dimensional geometry characteristic of rolling K-vector gratings and turning gratings formed in thin films (2 to 4 microns) using a birefringent control layer based on LCP and LPP. In some embodiments, the LCP or LPP based birefringence control layer further comprises dichroic dyes, chiral dopants for implementing narrow or broadband cholesteric filters, twisted retarders, or negative c-plate retarders. In many embodiments, an LCP or LPP based birefringence control layer provides a quarter-wave or half-wave retardation layer.

In some embodiments, the birefringent control layer is formed of a multilayer structure combining an isotropic refractive index layer and an anisotropic refractive index layer (as shown in fig. 4). In fig. 4, the multilayer structure 400 includes

isotropic layers

401, 402 and anisotropic refractive index layers 403, 404. In some embodiments, the multilayer stack may include a large number of layers such as, but not limited to, tens or hundreds of layers. Figure 5 conceptually illustrates a multilayer structure 500, the multilayer structure 500 including

isotropic layers

501, 502 and anisotropic refractive index layers 503, 504 in combination with a birefringent grating layer 505. Improved control of the reflectivity of P-polarized light is possible when the birefringence is on the same order of magnitude as the in-plane refractive index variation between adjacent material layers in the stack. Generally, in isotropic materials, Brewster's law indicates that for any interface there is an angle of incidence (Brewster angle) at which its P-polarized reflectivity disappears. However, at other angles, the reflectivity may increase dramatically. The limitation imposed by the Brewster angle can be overcome by applying the basic principles discussed by Weber et al in "Giant Bireframing Optics in multilayered Polymer Mirrors" as disclosed in Science, Vol 287, p 3/31/2000, p 2451-2456. Because the optical properties of the system of isotropic/anisotropic refractive index layers are based on the fundamental physics of interfacial reflection and phase thickness rather than on a specific multilayer interference stack design, new design freedom is possible. The design for wide-angle broadband applications is simplified if the brewster angle limitation is eliminated, especially for birefringent control layers immersed in high refractive index media such as waveguide substrates. A further advantage with waveguide displays is that color fidelity can be maintained for all angles of incidence and polarization.

The birefringent grating will typically have a polarization rotation characteristic that varies with the angular wavelength. The birefringence control layer may be used to modify the angular, spectral, or polarization properties of the waveguide. In some embodiments, the interaction of light with the birefringence control layer may provide an efficient angular bandwidth variation along the waveguide. In many embodiments, the interaction of light with the birefringence control layer can provide an efficient spectral bandwidth variation along the waveguide. In several embodiments, the interaction of light with the birefringence control layer can provide polarization rotation along the waveguide. In various embodiments, the grating birefringence can be varied across the waveguide by spatially varying the composition of the liquid crystal polymer mixture during grating fabrication. In some embodiments, the birefringence control layer may provide a change in birefringence in at least one direction in the plane of the waveguide substrate. The birefringent control layer may also provide a means for optimizing optical transmission (for different polarizations) within the waveguide. In many embodiments, the birefringent control layer may provide a change in transmission in at least one direction in the plane of the waveguide substrate. In several embodiments, the birefringence control layer may provide an angular dependence of at least one of the beam transmission or the polarization rotation in at least one direction in the plane of the waveguide substrate. In various embodiments, the birefringence control layer may provide a spectral dependence of at least one of beam transmission or polarization rotation in at least one direction in the plane of the waveguide substrate.

In many embodiments, birefringent gratings may provide input couplers, turning gratings, and output gratings in a wide range of waveguide architectures. FIG. 6 conceptually illustrates a plan view of a dual expansion waveguide having a birefringent control layer, in accordance with an embodiment of the present invention. In the illustrated embodiment, the waveguide 600 includes an optical substrate 601, the optical substrate 601 including an input grating 602, a turning grating 603, and an output grating 604 covered by polarization control layers 605, 606, 607, respectively.

In some embodiments, the present invention provides a polarization-maintaining, wide-angle birefringence control layer for modifying the polarization output of a waveguide to balance the birefringence of an external optical element used with the waveguide. Figure 7 conceptually illustrates an embodiment of the present invention directed to reflecting a collimated image off the windshield to the automobile HUD in the eye movement range. Any windshield curvature will typically result in aberrations and other geometric distortions that cannot be corrected in certain waveguide implementations where the beam is required to remain substantially collimated. One solution to this problem is to mount a corrective element, which may be a conventional refractive or diffractive element, near the output surface of the waveguide. In such implementations, the birefringence correction component can avoid interfering with the light path originating from the waveguide and can be achromatic. The compensator technology used can provide spatially varying configurations, low haze and high transmission. In the illustrated embodiment of fig. 7, the waveguide 700 includes: an optical substrate 701, the optical substrate 701 comprising a grating coupler 702 for deflecting light 703 from an external source of image modulated light (not shown) into a TIR path 704 in the waveguide; a birefringent grating 705 for providing beam expansion in a first direction and extracting light from the waveguide; and a birefringent control layer 706. The device 700 further comprises an optical element 707, the optical element 707 being arranged close to the waveguide for correcting geometrical distortions and other aberrations introduced by reflections at the windshield. In some embodiments, the optical element 707 is a refractive lens. In other embodiments, the optical element 707 may be a diffractive lens. For a wide field of view HUD that provides a large eye movement range, the corrector will typically have a large footprint with a horizontal dimension (along the dashboard) of up to 400 mm. However, if the corrector is molded from plastic, it will tend to suffer from birefringence. Thus, in the embodiment of fig. 7, the birefringence control element 706 may be designed to compensate for both the grating polarization and the polarization rotation introduced by the optical element 707. Referring again to FIG. 7, assume an initial polarization state corresponding to P-polarization. The polarization state after propagation through the birefringent grating, the birefringent control layer and the correction element is indicated by

reference

708 and 711. The interaction of light with the birefringent control layer near the grating interaction region along the TIR path is represented by the polarization state. In the embodiment of fig. 7, the polarizations of the light 712, 713 extracted by the gratings are aligned parallel to the input polarization vector. In some embodiments, the birefringent control layer 706 may be configured to rotate the output light polarization vector through ninety degrees.

In some embodiments, the birefringence control layer may be provided by various techniques using mechanical, thermal or electromagnetic treatment of the substrate. For example, in some embodiments, the birefringence control layer is formed by applying a mechanical stress that varies spatially across the surface of the optical substrate. FIG. 8 conceptually illustrates an apparatus 800 for aligning a birefringence control layer 801 that exerts forces in the directions indicated by 802-805, resulting in an anisotropic birefringence profile 806. In many embodiments, not all of the illustrated forces need be applied to the layer. In some embodiments, the birefringent control layer 801 is formed by inducing a thermal gradient in the optical substrate. In various embodiments, the birefringent control layer 801 is provided by an HPDLC grating in which the LC directors are aligned using an electric or magnetic field during curing. In several embodiments, two or more of the above techniques may be combined.

Fabrication of waveguides implementing birefringent control layers

The invention also provides a method and apparatus for manufacturing a waveguide comprising a birefringent grating and a birefringent control layer. The construction and arrangement of the devices and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., to improve process efficiency and quality of the finished waveguide, minimize process variation, monitor the process, and other additional steps). Any process step involving the formation of a layer should be understood to cover a plurality of such layers. For example, where a process step of recording a grating layer is described, this step may be extended to recording a stack comprising two or more grating layers. Accordingly, all such modifications are intended to be included within the scope of this disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design of the process equipment, operating conditions and arrangements of the exemplary embodiments without departing from the scope of the present disclosure. For the purpose of explaining the present invention, the description of the process will refer to a birefringence controlling layer based on a liquid crystal polymer material system as described above. However, it should be clear from the description that these processes may be based on any implementation of the birefringence control layer described herein.

Fig. 9A-9F conceptually illustrate process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringent control layer, according to various embodiments of the present invention. Fig. 9A shows a first step 900 of providing a first transparent substrate 901. Fig. 9B shows an apparatus 910 for applying a holographic recording material to a substrate 901. In the illustrated embodiment, the apparatus 910 includes a coating apparatus 911 that provides a spray pattern 912, the spray pattern 912 forming a layer 913 of grating recording material on the substrate 901. In some embodiments, the spray pattern may comprise a narrow jet or patch (blade) that is swept or stepped across the surface to be coated. In several embodiments, the spray pattern may comprise a divergent jet for simultaneously covering a large area of the surface. In various embodiments, the coating apparatus may be used in conjunction with one or more masters for providing selective coating of regions of a surface. In many embodiments, the coating apparatus is based on industry standard spin-on or inkjet printing processes.

Figure 9C conceptually illustrates an apparatus 920 for exposing a layer of grating recording material to form a grating layer, in accordance with embodiments of the present invention. In the illustrated embodiment, the apparatus 920 includes a master grating 921 and a laser 922 for contacting that replicate the grating in the recording material. As shown, the master grating 921 diffracts incident light 923 to provide zeroth order 924 and diffracted light 925, which zeroth order 924 and diffracted light 925 interfere within the grating material layer to form a grating layer 926. The apparatus may have further features such as, but not limited to, diaphragms and masters for overcoming stray light from higher diffraction orders or other sources. In some embodiments, several gratings may be recorded into a single layer using the principle of multiplexed holograms. Figure 9D conceptually illustrates a device 930 for applying a layer of liquid crystal polymer material onto a grating layer, in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 930 comprises a coating apparatus 931 configured to deliver a spray pattern 932 to form a material layer 933. The coating apparatus 931 may have similar features to the coating apparatus used to apply the grating recording material. Figure 9E conceptually illustrates an apparatus 940 for providing an aligned layer of liquid crystal polymer material, in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 940 includes a UV source (which may include collimating, beam steering, and beam shaping optics, depending on the specific requirements of a given application) 941 that provides directed UV light 942 for forming the aligned LC polymer layer 943. Fig. 9F conceptually illustrates the completed waveguide 950 after the step of applying the second substrate 951 over the aligned liquid crystal polymer layer 943.

In some embodiments, the exposure of the grating recording material may use a conventional cross-beam recording process instead of the mastering process described above. In many embodiments, further processing of the grating layer may include annealing, heat treatment, and/or other processes for stabilizing the optical properties of the grating layer. In some embodiments, an electrode coating may be applied to the substrate. In many embodiments, a protective transparent layer may be applied over the grating layer after exposure. In various embodiments, the liquid crystal polymer material is based on the LCP, LPP material system discussed above. In several embodiments, the alignment of the liquid crystal polymer may result in the alignment of the liquid crystal director being parallel to the UV beam direction. In other embodiments, the alignment is at ninety degrees to the UV beam direction. In some embodiments, the second transparent substrate may be replaced with a protective layer applied using a coating apparatus.

10A-10F conceptually illustrate process steps and apparatus for fabricating a waveguide including a birefringence control layer and a birefringent grating applied to an outer surface of the waveguide, in accordance with various embodiments of the present invention. Figure 10A conceptually illustrates a first step 1000 of providing a first transparent substrate 1001, in accordance with embodiments of the present invention. FIG. 10B conceptually illustrates an apparatus 1010 for applying a holographic recording material to a substrate, in accordance with embodiments of the present invention. In the illustrated embodiment, the apparatus 1010 includes a coating apparatus 1011 that provides a spray pattern 1012, which spray pattern 1012 forms a layer 1013 of a lenticular recording material on a substrate 1001. Figure 10C conceptually illustrates an apparatus 1020 for exposing a layer of grating recording material to form a grating layer, in accordance with embodiments of the present invention. In the illustrated embodiment, the device 1020 includes a master grating 1021 for contact that replicates the grating in the recording material and a laser 1022. As shown, the master 1021 converts the light 1023 from the lasers 1022 into zero-order 1024 and diffracted light 1025, the zero-order 1024 and diffracted light 1025 interfering within the grating material layer 1013 to form a grating layer 1026. Fig. 10D conceptually illustrates a partially completed waveguide 1030 after the step of applying the second substrate 1031 over the exposed grating layer, in accordance with an embodiment of the present invention. Figure 10E conceptually illustrates an apparatus 1040 for applying a layer of liquid crystal polymer material onto a second substrate, in accordance with embodiments of the invention. In the illustrated embodiment, the apparatus 1040 includes a spray applicator 1041 for delivering a spray pattern 1042 to form a material layer 1043. Figure 10F conceptually illustrates an apparatus 1050 for aligning liquid crystal polymer material, in accordance with embodiments of the present invention. In the illustrated embodiment, device 1050 includes a UV source 1051, where UV source 1051 provides directed UV light 1052 for forming aligned liquid crystal polymer layer 1053, where directed UV light 1052 may be configured to realign the LC directors of grating layer 1026.

11A-11F conceptually illustrate process steps and apparatus for fabricating a waveguide including a birefringent grating and a birefringent control layer, according to various embodiments of the present invention. Unlike the above-described embodiments, the step of forming the birefringent control layer may be performed before recording the grating layer formed above the birefringent control layer. Figure 11A conceptually illustrates a first step 1100 of providing a first transparent substrate 1101. Figure 11B conceptually illustrates an apparatus 1110 for applying a layer of liquid crystal polymer material onto a first substrate, in accordance with embodiments of the invention. In the illustrated embodiment, the apparatus 1110 includes a coating apparatus 1111 configured to deliver a spray pattern 1112 to form a material layer 1113. Figure 11C conceptually illustrates an apparatus 1120 for aligning liquid crystal polymer material, in accordance with an embodiment of the present invention. In the illustrated embodiment, the apparatus 1120 includes a UV source 1121 that provides directed UV light 1122 that is used to form the aligned liquid crystal polymer layer 1123. Figure 11D conceptually illustrates an apparatus 1130 of applying a holographic recording material to a substrate, in accordance with embodiments of the present invention. In the illustrated embodiment, the apparatus 1130 includes a coating apparatus 1131 for providing a spray pattern 1132 to form a layer 1133 of grating recording material on top of the liquid crystal polymer layer 1123. Figure 11E conceptually illustrates an apparatus 1140 for exposing a layer of grating recording material to form a grating layer, according to an embodiment of the present invention. In the illustrated embodiment, the apparatus 1140 includes a master grating 1141 and a laser 1142 for contact that replicate the grating in the recording material. As shown, the master grating 1141 converts light 1142 from the laser into zero order 1143 and diffracted light 1144, which zero order 1143 and diffracted light 1144 interfere in the grating material layer 1133 to form a grating layer 1123 arranged by a liquid crystal polymer material layer 1123. Figure 11F conceptually illustrates the completed waveguide 1150 after the step of applying a second substrate 1151 over the exposed grating layer, in accordance with embodiments of the present invention.

FIG. 12 conceptually illustrates a flow chart that illustrates a method of manufacturing a waveguide that includes a birefringent grating and a birefringent control layer, in accordance with an embodiment of the present invention. Referring to fig. 12, method 1200 includes providing (1201) a first transparent substrate. A layer of grating recording material may be deposited (1202) onto the substrate. The layer of grating recording material may be exposed 1203 to form a grating layer. A layer of liquid crystal polymer material may be deposited (1204) onto the grating layer. Oriented UV light may be used to align (1205) the liquid crystal polymer material. A second transparent substrate may be applied 1206 over the alignment layer.

FIG. 13 conceptually illustrates a flow chart that illustrates a method of manufacturing a waveguide that includes a birefringence control layer and a birefringence grating applied to an outer surface of the waveguide, in accordance with an embodiment of the present invention. Referring to fig. 13, method 1300 includes providing (1301) a first transparent substrate. A layer of grating recording material may be deposited 1302 onto a substrate. The layer of grating recording material may be exposed 1303 to form a grating layer. A second transparent substrate may be applied 1304 over the exposed grating layer. A layer of liquid crystal polymer material may be deposited (1305) onto a second transparent substrate. The liquid crystal polymer material may be aligned 1306 using directed UV light.

Figure 14 conceptually illustrates a flowchart that illustrates a method of manufacturing a waveguide that includes a birefringent grating and a birefringent control layer, where forming the birefringent control layer is performed before recording the grating layer, in accordance with an embodiment of the present invention. Referring to fig. 14, a method 1400 includes providing 1401 a first transparent substrate. A layer of liquid crystal polymer material may be deposited 1402 onto a substrate. Aligned UV light can be used to align (1403) the liquid crystal polymer material. A layer of grating recording material may be deposited (1404) onto the aligned liquid crystal polymer material. The layer of grating recording material may be exposed (1405) to form a grating layer. A second transparent substrate can be applied 1406 over the grating layer.

While fig. 12-14 illustrate specific processes for fabricating waveguides containing birefringent gratings and birefringent control layers, many other fabrication processes and devices may be implemented to form such waveguides according to various embodiments of the present invention. For example, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design of the process equipment, operating conditions and arrangements of the exemplary embodiments without departing from the scope of the present disclosure.

Additional embodiments and applications

In some embodiments, a polarization-maintaining, wide-angle, highly reflective waveguide cladding with polarization that compensates for grating birefringence may be implemented. One such embodiment is shown in fig. 15. In the illustrated embodiment, the waveguide 1500 includes a waveguide substrate 1501 including a birefringent grating 1502 and a birefringence control layer 1503 overlying the waveguide substrate 1501. As shown, interaction of the guided light 1504 with the birefringent control layer 1503 at the interface of the birefringent control layer 1503 and the waveguide substrate 1501 causes its polarization to rotate from the state indicated by symbol 1505 (resulting from previous interaction with the grating) to the state indicated by 1506 (having a desired orientation for the next interaction with the grating, e.g., having an orientation that provides a predefined diffraction efficiency at some predefined point along the grating).

In many embodiments, a compact and efficient birefringent control layer for isolating the waveguide from its environment while ensuring efficient confinement of the waveguide beam may be achieved. Fig. 16 illustrates one such embodiment. In the illustrated embodiment, the environmentally isolated waveguide 1600 includes a waveguide substrate 1601 including a birefringent grating 1602 and a birefringent control layer 1603 overlying the waveguide substrate 1601. As shown, interaction of the guided light 1604 with the birefringent control layer 1603 at the interface of the birefringent control layer 1603 and the waveguide substrate 1601 causes its polarization to rotate from the state indicated by the symbol 1605 to the state indicated by 1606. Environmental isolation of the waveguide may be provided by designing the birefringent control layer 1603 such that total internal reflection occurs at the interface 1607 between the birefringent control layer 1603 and the waveguide substrate 1601. In some embodiments, environmental isolation is provided by designing the birefringent control layer to have a gradient index of refraction characteristic such that only a small fraction of the light directed at the air interface of the birefringent control layer is reflected. In several embodiments, the birefringence controlling layer may comprise a single GRIN layer. In various embodiments, the GRIN layer may be based on the embodiments disclosed in U.S. provisional patent application No. 62/123,282 entitled "NEAR EYE DISPLAY use recording INDEX options" and U.S. provisional patent application No. 62/124,550 entitled "WAVEGUIDE DISPLAY USE recording INDEX options".

Figure 17 conceptually illustrates an apparatus 1700, in accordance with an embodiment of the invention, which apparatus 1700 may be used in conjunction with some of the methods described above, for fabricating a structure that includes a birefringent grating layer 1701 overlying a birefringent control layer 1702. In fig. 17, the substrate supporting the birefringence control layer is not shown. The constructed beam indicated by

rays

1703, 1704 may be provided by a master grating or a cross-beam holographic recording setup. As shown, the formation beam propagates through the birefringent control layer 1702. In many embodiments, the constructed beam is in the visible band. In some embodiments, the construction beam is in the UV band.

FIG. 18 conceptually illustrates an apparatus 1800, which apparatus 1800 may be used in conjunction with some of the methods described above, for fabricating a structure that includes a birefringent control layer 1801 overlying a birefringent grating layer 1802, in accordance with an embodiment of the present invention. In fig. 18, the substrate supporting the grating layer is not shown. The direction of the recording beam is indicated by 1803. In many embodiments, the birefringence controlling layer is a liquid crystal polymer material system that uses a directed UV beam for alignment. In some embodiments in which the grating is recorded in a polymer and liquid crystal material system, the exposed grating may be erased during the process of aligning the birefringent control layer by applying an external stimulus such as heat, an electric or magnetic field, or light, to effectively produce the isotropic phase of the liquid crystal.

Figure 19 conceptually illustrates a cross-section of a waveguide 1900 that includes

substrates

1901, 1902 sandwiching a grating layer 1903. As shown, source 1904 emits collimated light 1905A, which collimated light 1905A is coupled by the grating layer into a Total Internal Reflection (TIR) path indicated by

rays

1905B, 1905C, and extracted by grating layer 1903 into output ray path 1905D. In the illustrated embodiment, the source 1904 can be a variety of light sources including, but not limited to, a laser or an LED.

Figure 20 conceptually illustrates a waveguide similar to that of figure 19, having a quarter wave polarizing layer inserted by replacing the substrate 1902 with a quarter wave film 2001 sandwiched by

substrates

2002, 2003, in accordance with an embodiment of the present invention. The quarter wave polarizing layer may benefit the holographic waveguide design in two ways. First, it can reduce the repetitive interaction (outcoupling) of the rolling K-vector (RKV) input grating to increase the overall coupling efficiency of the input grating. Second, it can continuously mix the polarization of the light entering the turning grating and the output grating to provide better extraction. The quarter wave layer may be located on the waveguide surface along the light from the input grating. In general, the waveguide surface may comprise one of a TIR surface of the wave or some intermediate surface formed inside the waveguide. The optical properties of the quarter-wave layer can be optimized for the "waveguide angle" (i.e., the angle in the glass that exceeds the TIR angle). In some embodiments, the central field is designed to be approximately 55 degrees in glass (corresponding to an index of refraction of approximately 1.51 at a wavelength of 532 nm). In many embodiments, to optimize the performance of the red, green, and blue emitting waveguides, optimizations for red, green, and blue may be used. As will be shown in the embodiments to be described, there are several different ways of incorporating a quarter-wave film within a waveguide. In the following examples we generally refer to a quarter wave polarizing layer provided by a Liquid Crystal Polymer (LCP) material. However, it should be understood that other materials may be used in the application of the present invention.

Figure 21 conceptually illustrates a schematic cross-sectional view 2100 showing a portion of a waveguide, in accordance with an embodiment of the invention, to illustrate how the use of a quarter-wave polarizing layer with an RKV grating can overcome the problem of unwanted extraction of light along the propagation path in the input grating portion of the waveguide. An input light comprising P-polarized light 2101A is illustrated as being coupled by the grating layer into one of the TIR paths in the waveguide as indicated by rays 2101B-2101L. The waveguide grating has a rolling K vector, an example of which is schematically illustrated by vectors 2102A-2102C occurring at three points along the length of the waveguide. In the illustrated embodiment, light 2101A diffractively coupled into TIR by the input grating is P-polarized with respect to the grating. In many embodiments, the TIR angle may be nominally 55 degrees in glass. Upon transmission through the quarter-wave layer, the polarization of the light changes from P to circular polarization (2101C). After TIR at the lower surface of the waveguide, the polarization becomes circularly polarized light in the opposite direction (2101D) so that after passing through the quarter wave layer on its upstream path, it becomes S polarized with respect to the grating (2101E). Since the S-polarized light is both non-Bragg (off-Bragg) and "unpolarized" (since the grating has zero or low diffraction efficiency for S), the S-polarized light passes through the grating without being polarized (2101F) or substantial loss. The light then undergoes TIR a second time (2101G) thus preserving its S polarization. Thus, with respect to a P-polarization sensitive grating, the light 2101G is now Bragg (on-Bragg), but still unpolarized. Thus, the light passes through the grating without diffraction (2101H). At this position, RKV (2102B) is slightly scrolled relative to RKV (2102A) near the point of light entry on the I/P grating. If the light is "polarized", the "rolling" effect of RKV will be small, and so the light will be strongly outcoupled. The S-polarized light passing through the grating goes through another complete period (2101H-2101M) in a similar manner to the period indicated by rays 2101B-2101G, and then returns to the P-polarized state for the next (2101M) Bragg interaction at the grating region with the K vector 2102C. At this point, the light has performed two complete TIR bounce cycles down the waveguide, increasing the K vector and the angular separation of the angles of incidence at the grating, which strongly reduces the bragg interaction.

To further illustrate the embodiment of fig. 21, consider light at 55 degrees TIR angle in a 1mm thick waveguide, with a projector relief (projector relief) of 20mm (distance of projector from input grating), and a projector exit pupil of nominal 4.3mm diameter: the first interaction with the grating occurs approximately 2.85mm down the waveguide. This equates to an angle of 8.1 degrees at a 20mm projector relief. For comparison, the FWHM angular bandwidth of a typical 1.6um grating is about 12 degrees in air (depending on the recipe), i.e. the angle subtended by the pupil is not much larger than the half width of the lens. This results in strong out-coupling if the polarization is not changed to S-polarization as described above. In practice, the use of a quarter-wave layer doubles the TIR length to approximately 5.7 mm. This offset is equivalent to about 15.9 degrees (greater than the angular bandwidth of most waveguide gratings), thereby reducing the out-coupling interaction loss from the waveguide.

Figure 22 conceptually illustrates a polarizing layer architecture 2200 comprising LCP quarter wave cells and Reactive Monomer Liquid Crystal Mixture (RMLCM) cells separated by an index matching oil layer (2201), according to an embodiment of the present invention. The LCP unit includes a substrate 2202 and an LCP film 2203. The RMLCM unit includes

substrates

2204, 2205 sandwiching a RMLCM layer 2206. This configuration has the following advantages: the index-matched oil bond may provide a non-permanent bond to allow the polarization unit to be installed and removed for testing purposes. Adhesive may also be applied at the (pinned) edges for semi-permanent bonding. In some embodiments, the oil layer may be provided using oil-filled cells.

Figure 23 conceptually illustrates an example of a polarizing architecture 2300 based on grating cells having a RMLCM grating material layer 2301 in direct contact with a bare LCP film 2302, according to an embodiment of the invention. The two films are sandwiched by

substrates

2303, 2304. This is a simple and cost-effective solution for implementing LCP layers. Maintaining thickness control of the RMLCM layer using spacer beads can be difficult if the beads are embedded directly on the LCP layer. The embodiment of fig. 23 may require careful matching of the material properties of the RMLCM and LCP to avoid detrimental interactions between the RMLCM and LCP layers. In many embodiments, holographic exposure of the RMLCM layer may be applied directly in the RMLCM, without passing through the LCP layer. In some embodiments, the polarization rotation of the LCP layer may be pre-compensated if exposure configuration through the LCP layer is unavoidable.

Figure 24 conceptually illustrates a cross-sectional view that schematically shows an example of a polarization layer architecture 2400 in which a bare LCP layer is bonded to a bare RMLCM layer, in accordance with an embodiment of the present invention. The device includes an upper substrate 2401, a bare LCP film 2402, an adhesive layer 2403, an exposed RMLCM layer 2404, and a lower substrate 2405. In many embodiments, the adhesive layer may be a Norland NOA65 adhesive or a similar adhesive.

Fig. 25 conceptually illustrates a cross-sectional view that schematically shows an example of a polarization layer architecture 2500 using an RMLCM layer as the polarization layer, in accordance with an embodiment of the present invention. The device includes an upper substrate 2501, an upper RMLCM layer 2502, a transparent spacer 2503, a lower RMLCM layer 2504, and a lower substrate 2505. One of the RMLCM layers can be used not only as a grating material, but also as a polarization rotating layer, taking advantage of the inherent birefringence properties of the RMLCM material. The "polarization rotating grating" should have a period and/or k-vector orientation such that diffraction is minimal. In some embodiments, the RMLCM layer may be configured as a sub-wavelength grating. In some embodiments, the RMLCM layer may be disposed sandwiched between two release layers, such that after the layer is cured, it may be removed and reapplied elsewhere.

Figure 26 conceptually illustrates an example of a polarization layer architecture 2600 that includes features for compensating for polarization rotation introduced by a birefringent grating, in accordance with an embodiment of the present invention. The device includes an upper substrate 2601, a polarization control layer 2602, a transparent substrate 2603, a grating layer 2604, and a lower substrate 2605. The grating layer includes a first grating 2606A and a second grating 2606B separated by a transparent region 2607. In some embodiments, the transparent region may be a polymer having a refractive index similar to that of the substrate. In many embodiments, other low index materials may be used to provide the transparent region. The polarization control layer includes quarter-

wave retarding regions

2608A, 2608B and polarization compensation regions that balance the polarization rotation introduced by the birefringent grating 2606A (in the case of guided light propagating from grating 2606A to grating 2606B).

Figure 27 conceptually illustrates a plan view of a waveguide display 2700 that schematically shows features that incorporate the embodiments of figure 26, in accordance with embodiments of the present invention. Waveguide display 2700 includes a waveguide substrate 2701, an input grating 2702, a turning grating 2703, and an output grating 2704. In accordance with the principles of the embodiment of FIG. 26, the

polarization control regions

2705, 2706 apply compensation to the grating depolarization.

Fig. 28 conceptually illustrates a cross-sectional view that schematically shows an example of a polarization layer architecture 2800 that includes an upper substrate 2801, an LCP layer 2802 with a hard encapsulation layer 2803, an RMLCM layer 2804, and a lower substrate 2805, in accordance with an embodiment of the present invention. In many embodiments, the hard encapsulation layer or film may be designed to protect the fragile LCP film from mechanical contact so that standard cleaning procedures will not damage the film. Advantageously, the hard encapsulant layer may employ a material that is resistant to the spacer beads being pushed into it by the lamination process, and chemically resistant to the index matching oil and adhesive.

Fig. 29 conceptually illustrates a cross-sectional view schematically showing an example of a polarizer layer architecture 2900 including an upper substrate 2901, an LCP layer 2902 having a soft encapsulant layer 2903, an RMLCM layer 2904, and a lower substrate 2905, in accordance with an embodiment of the present invention. The polarization alignment film may be encapsulated with a soft encapsulant layer or film designed to protect the fragile LCP film from mechanical contact so that standard cleaning procedures, such as mopping with, for example, isopropyl alcohol, will not damage the film. In some embodiments, the soft seal may provide some resistance to the spacer beads during the lamination process.

Figure 30 conceptually illustrates a plan view of a first example 3000 that schematically illustrates a two-region polymer film, in accordance with an embodiment of the present invention. This example uses a non-encapsulating LCP film 3001 supported by a 0.5mm thick Eagle XG substrate of dimensions 77.2mm x 47.2 mm. Region 1 is characterized by a fast axis of 75 ° relative to horizontal for a wavelength of 524nm, and by a quarter-wave retardation at 55 ° internal glass angle, 45 ° ellipticity ± 5 °. Region 2 is characterized by a fast axis of 105 ° relative to horizontal, and by a quarter-wave retardation at 55 ° internal glass angle, 45 ° ellipticity ± 5 °, for a wavelength of 524 nm. Typically, zones 1 and 2 extend horizontally to the midpoint ± 2 mm.

Figure 31 conceptually illustrates a plan view of a second example 3100 that schematically illustrates a two-region polymer film, in accordance with an embodiment of the present invention. This example uses encapsulation of an LCP layer 3101 through a protective film 3102, supported by a 0.5mm thick Eagle XG substrate of dimensions 77.2mm by 47.2 mm. Region 1 is characterized by a fast axis of 75 ° relative to horizontal for a wavelength of 524nm, and by a quarter-wave retardation at 55 ° internal glass angle, 45 ° ellipticity ± 5 °. Region 2 is characterized by a fast axis of 105 ° relative to horizontal, and by a quarter-wave retardation at 55 ° internal glass angle, 45 ° ellipticity ± 5 °, for a wavelength of 524 nm. Typically, zones 1 and 2 extend horizontally to the midpoint ± 2 mm. The encapsulating layer may encapsulate the polarizing layer such that performance is not affected when covered by an oil layer such as Cargille series A having a refractive index of 1.516. The encapsulating layer may seal the polarizing layer so that the performance is not affected when covered by an additional layer of liquid crystal based photopolymer.

Figure 32 conceptually illustrates a plan view of a third example 3200 that schematically illustrates a two-region polymer film, in accordance with an embodiment of the present invention. This example uses glass encapsulation of LCP. A 0.5mm thick Eagle XG substrate measuring 77.2mm by 47.2mm supports the LCP layer 3201, adhesive layer 3202 and 0.2mm thick Willow glass cover 3203. Region 1 is characterized by a fast axis of 75 ° relative to horizontal for a wavelength of 524nm, and by a quarter-wave retardation at 55 ° internal glass angle, 45 ° ellipticity ± 5 °. Region 2 is characterized by a fast axis of 105 ° relative to horizontal, and by a quarter-wave retardation at 55 ° internal glass angle, 45 ° ellipticity ± 5 °, for a wavelength of 524 nm. Advantageously, the glass used for LCP encapsulation is 0.5mm eagleXG or 0.2mm Willow glass. Typically, zones 1 and 2 extend horizontally to the midpoint ± 2 mm.

Figure 33 conceptually illustrates a diagram showing the transparent aperture layout 3300 of the embodiment illustrated in figures 30-32, according to an embodiment of the present invention. The transparent aperture is highlighted by a dashed line. All dimensions are in mm.

Figure 34 conceptually illustrates a plan view 3400 that schematically shows a waveguide 3401 that includes an input grating 3402, a turning grating 3403, and an output grating 3404 based on the embodiments of figures 30-33 that include K vectors and alignment layer fast axis directions for each grating, according to an embodiment of the invention. As shown in fig. 34, the K vector and fast axis direction are for the input grating K vector: 30 degrees; for a turning grating, the K vector is: 270 degrees; and for the output raster K vector is: 150 degrees.

The above description covers only some of the possible embodiments in which an LCP layer (or equivalent retardation layer) may be combined with a RMLCM layer in a waveguide structure. In many of the above embodiments, the substrate may be made of 0.5mm thick Corning Eagle XG glass. In some embodiments, thinner or thicker substrates may be used. In several embodiments, the substrate may be made of plastic. In various embodiments, the substrate and the optical layer encapsulated by the substrate may be curved. Any of the embodiments may include additional layers for protection from chemical contamination or damage incurred during handling and manipulation. In some embodiments, additional substrate layers may be provided to achieve the desired waveguide thickness. In some embodiments, additional layers may be provided to perform at least one of illumination averaging spectral filtering, angular selective filtering, stray light control, and de-banding. In many embodiments, the bare LCP layer may be bonded directly to the bare RMLCM layer. In several embodiments, an intermediate substrate may be disposed between the LCP layer and the RMLCM layer. In various embodiments, the LCP layer may be combined with an unexposed layer of RMLCM material. In many embodiments, the LCP layer, with or without encapsulation, may have a haze characteristic of < 0.25% and preferably 0.1% or less. It should be noted that the cited haze properties are based on bulk material scattering and are independent of surface scattering losses, which are largely lost after immersion. The LCP and the encapsulating layer can withstand exposure to 100C (> 80C for thermal UM exposure). In many embodiments, the LCP encapsulating layer may be scratch resistant to allow the layer to be cleaned. In the above embodiments, there may be a constant retardation and no bubbles or voids within the transparent aperture of the membrane. The LCP and adhesive layers may match the optical flatness criteria met by the waveguide substrate.

A color waveguide according to the principles of the present invention will typically comprise a stack of monochromatic waveguides. The design may use a red waveguide layer, a green waveguide layer, and a blue waveguide layer, or alternatively, a red layer and a blue/green layer. In some embodiments, the gratings are all passive, that is, non-switching. In some embodiments, at least one of the gratings is switched. In some embodiments, the input gratings in each layer are switchable to avoid color crosstalk between the waveguide layers. In some embodiments, color crosstalk may be avoided by placing dichroic filters between the input grating regions of the red and blue waveguides and the blue and green waveguides. In some embodiments, the thickness of the birefringence control layer is optimized for the wavelength of light propagating within the waveguide to provide uniform birefringence compensation over the spectral bandwidth of the waveguide display. The wavelengths and spectral bandwidth bands of red, green, and blue wavelengths typically used in waveguide displays are red: 626 nm. + -. 9nm, green: 522nm plus or minus 18 nm; and blue: 452 nm. + -. 11 nm. In some embodiments, the thickness of the birefringent control layer is optimized for three color light.

In many embodiments, the birefringence control layer is provided by a sub-wavelength grating recorded in the HPDLC. Such gratings are known to exhibit form birefringence and may be configured to provide a range of polarization functions including quarter-wave and half-wave retardation. In some embodiments, the birefringence control layer is provided by a liquid crystal medium in which the LC director is aligned by illuminating the azo dye-doped alignment layer with polarized or unpolarized light. In many embodiments, the birefringent control layer is patterned to provide an LC director orientation pattern with a sub-micron resolution step size. In some embodiments, the birefringent control layer is treated to provide a continuous change in the orientation of the LC director. In several embodiments, a birefringence control layer provided by combining one or more of the above techniques is combined with a rubbing process or a polyimide alignment layer. In some embodiments, the birefringent control layer provides optical power. In many embodiments, the birefringent control layer provides a gradient index structure. In several embodiments, the birefringence control layer is provided by a stack comprising at least one HPDLC grating and at least one alignment layer. In many embodiments, the birefringent grating may have a rolling K-vector. The K vector is the vector aligned perpendicular to the grating plane (or fringes) that determines the optical efficiency for a given range of input and diffraction angles. The rolling K vector allows the angular bandwidth of the grating to be extended without requiring an increase in waveguide thickness. In many embodiments, the birefringent grating is a turning grating for providing exit pupil expansion. The inflected grating may be based on any of the embodiments disclosed in PCT application No. PCT/GB2016000181, entitled "WAVEGUIDE DISPLAY" and the embodiments discussed in the other references given above.

In some embodiments, the apparatus is used in a waveguide design to overcome the problem of laser banding. A waveguide according to the principles of the present invention may provide pupil shifting means for configuring light coupled into the waveguide such that the input grating has an efficient input aperture that varies with the TIR angle. Several embodiments of the pupil shifting arrangement will be described. The effect of the pupil shifting means is continuous light extraction from the waveguide through the set of output gratings to provide a substantially flat illumination profile for any light incidence angle at the input gratings. The pupil shifting means may be implemented using a birefringent control layer to vary at least one of amplitude, polarization, phase and wavefront shift in 3D space as the angle of incident light varies. In each case, the effect is to provide an effective aperture that can give uniform extraction across the output grating for any angle of incidence of light at the input grating. In some embodiments, a pupil shifting device is provided at least in part by: the optics of the input image generator according to various embodiments are designed to have a high Numerical Aperture (NA) variation that smoothly varies from the NA range that is high on one side of the microdisplay panel to a low NA range at the other side, such as similar to those disclosed in PCT application No.: PCT/GB2016000181, entitled "wavegide DISPLAY," the disclosure of which is incorporated herein in its entirety. Typically, microdisplays are reflective devices.

In some embodiments, the grating layer may be decomposed into individual layers. The multiple layers may then be laminated together into a single waveguide substrate. In many embodiments, the grating layer comprises several pieces, including an input coupler, a turning grating, and an output grating (or portions thereof), that are laminated together to form a single substrate waveguide. The pieces may be separated by optical glue or other transparent material with an index of refraction matching that of the pieces. In several embodiments, the grating layer may be formed via a cell fabrication process by creating cells of a desired grating thickness and vacuum filling each cell with SBG material for each of the input-coupler, the turning grating, and the output grating. In one embodiment, the cell is formed by positioning a plurality of glass plates having a gap between the glass plates that defines the desired grating thickness for the input coupler, the turning grating, and the output grating. In one embodiment, a cell can be made with multiple apertures such that separate apertures are filled with different SBG material packets. Any intervening spaces may then be separated by a separation material (e.g., glue, oil, etc.) to define separated regions. In one embodiment, the SBG material may be spin coated onto the substrate and then covered by a second substrate after the material is cured. By using a turning grating, the waveguide display advantageously requires fewer layers than previous systems and methods of displaying information according to some embodiments. In addition, by using a turning grating, light can travel in a single rectangular prism defined by the outer surface of the waveguide by total internal reflection within the waveguide, while achieving dual pupil expansion. In another embodiment, the input coupler, grating, may be produced by two waves of light interfering at an angle within the substrate to produce a holographic wavefront, thereby producing light and dark fringes that are disposed at a desired angle in the waveguide substrate. In some embodiments, the grating in a given layer is recorded in a step-wise manner by scanning or stepping the recording laser beam across the grating area. In some embodiments, the gratings are recorded using a master and contact printing process currently used in the holographic printing industry.

In many embodiments, the grating is a Bragg grating recorded in Holographic Polymer Dispersed Liquid Crystal (HPDLC) as already discussed, although SBG may also be recorded in other materials. In one embodiment, SBG is recorded in a homogeneous modulating material such as policrypts or POLIPHEM with a solid liquid crystal matrix dispersed in a liquid polymer. SBGs may be switching or non-switching in nature. In its non-switching form, SBG has advantages over conventional holographic photopolymer materials that are capable of providing high refractive index modulation due to their liquid crystal composition. Exemplary homogeneously modulated liquid crystal-polymer material systems are disclosed in U.S. patent application publication No. US2007/0019152 to Caputo et al and PCT application No. PCT/EP2005/006950 to Stumpe et al, both of which are incorporated herein by reference in their entirety. A uniformly modulated grating is characterized by high refractive index modulation (and therefore high diffraction efficiency) and low scattering. In some embodiments, at least one of the gratings is a surface topography grating. In some embodiments, at least one of the gratings is a thin (or Raman-Nath) hologram.

In some embodiments, the grating is recorded in a reverse mode HPDLC material. Reverse mode HPDLC differs from conventional HPDLC in that when no electric field is applied, the grating is passive, whereas in the presence of an electric field, the grating becomes diffractive. The reverse mode HPDLC may be based on any of the formulations and processes disclosed in PCT application No. PCT/GB2012/000680 entitled "IMPROVEMENTS TO HOLOGRAPHIC POLYMER DISPERSED LIQUID CRYSTAL MATERIALS AND DEVICES". The grating may be recorded in any of the above material systems, but is used in a passive (non-switching) mode. The manufacturing process may be the same as for the switch, but the electrode coating stage is omitted. An LC polymer material system may be used for its high refractive index modulation. In some embodiments, the grating is recorded in the HPDLC, but is not switched.

In many embodiments, a waveguide display according to the principles of the present invention may be integrated within a window, for example, a windshield integrated HUD for road vehicle applications. IN some embodiments, the window integrated DISPLAY may be based on the embodiments and teachings disclosed IN U.S. provisional patent application No. 62/125,064 entitled "OPTICAL window DISPLAYS FOR integrating IN WINDOWS" and U.S. patent application No. 15/543,016 entitled "integrated window DISPLAYS". In some embodiments, a WAVEGUIDE display in accordance with the principles of the present invention may include a light pipe for providing beam expansion in one direction based on the embodiment disclosed in U.S. patent application No.:15/558,409 entitled WAVEGUIDE DEVICE organizing A LIGHT PIPE. In some embodiments, the input image generator may be based on a laser scanner as disclosed in U.S. patent No.9,075,184 entitled "COMPACT EDGE illuninated DIFFRACTIVE DISPLAY". Embodiments of the invention may be used for a wide range of displays, including HMDs for AR and VR, head mounted displays, projection displays, Heads Up Displays (HUDs), Heads Down Displays (HDDs), autostereoscopic displays and other 3D displays. Some of the embodiments and teachings of this disclosure may be applied in waveguide sensors such as, for example, eye trackers, fingerprint scanners, and LIDAR systems, as well as in illuminators and backlights.

It should be emphasized that the figures are exemplary and the dimensions have been exaggerated. For example, the thickness of the SBG layer has been greatly exaggerated. An optical device based on any of the above embodiments may be implemented using a glass substrate utilizing the materials and processes disclosed in PCT application No. PCT/GB2012/000680 entitled "advanced TO tall graphics POLYMER DISPERSED LIQUID required CRYSTAL MATERIALS AND DEVICES". In some embodiments, the dual expansion waveguide display may be curved.

While the specification has provided specific embodiments of the present invention, additional information regarding the technology can be found in the following patent applications, which are hereby incorporated by reference in their entirety: US patent No.9,075,184 entitled "COMPACT EDGE ILLUMINATED DIFFRACTIVE DISPLAY", US patent No.8,233,204 entitled "OPTIC DISPLAYS", PCT application No. US2006/04 14/620,969 entitled "COMPACT DISPLAYS", PCT application No. GB2012/000677 entitled "COMPACT AND APPARATUS FOR PROVIDING A TRANSPARENT DISPLAY", US patent application No. 13/317,468 entitled "COMPACT EDGE LUMINATED EYEGLASS DISPLAY", US patent application No. 13/869,866 entitled "HOLOGRAPHIC WIDE ANGLE DISPLAY", US patent application No. US 13/844,456 entitled "TRANSPARENT WAVEGUIDE DISPLAY", US patent application No. US 59638 entitled "WAVEGUIDE GRATING DEVICE", US patent application No. PARGES 15/553,120 entitled "DISPLACES ELECTRICALLY FOCUS TUNABLE LENS", US patent application No. GUSING A LIGHT PIPE entitled "DEVICE GUIDING A LIGHT PIPE", US patent application No. GUIDING A LIGHT PIPE entitled "METHOD 15/512,500, US provisional patent application No. 62/123,282 entitled "WAVEGUIDE DISPLAY USE SYSTEM INDENT OPTICS", US provisional patent application No. 62/124,550 entitled "OPENING WAVEGUIDE DISPLAY FOR INTEGRATION IN WINDOWS", US provisional patent application No. 62/125,064 entitled "ENVIRONMENT ISOLATED WAVEGUIDE DISPLAY", US provisional patent application No. 15/543,016, US provisional patent application No. 62/125,089 entitled "HOLOGRAPHIC WAVEGUIDE LIGHT FIELD DISPLAYS", US provisional patent application No. NANANANAND3628 entitled "LASILLUMINATION DEV DEVICE", US patent application No.8,224,133 entitled "PCT TRANSPLANT DEVICE No. PCT DEVICE No. 8298, US patent application No. 201PORTIONA DEVICE No. PCT DEVICE No. 000023, US patent application No. PCT DEVICE 82923, US patent application No. PCT DEVICE 829 PCT/GB2014/000197, PCT/GB2013/000210 entitled "APPLICATIC WAVEGUIDE EYE TRACKING", PCT application No. GB2013/000210 entitled "APPLICATIC WAVEGUIDE OPTIMACKER", US patent No. 2015/000274 entitled "APPLICATIC WAVEGUIDE VERTICAL FIELD OF VIEW IN HEAD UP PLAY USE AND WAVEGUIDE VERTICAL FIELD", US patent No.8,903,207 entitled "COMPACT WEARABLE DISPLAY" US patent No.8,639,072 entitled "COMPACT HOGRATED PLAY", US patent No.8,885,112 entitled "APPLICATION 2016038", US patent No. PCT/PLAYING 2016081 entitled "COMPACT HOGRAGRAGRATED HOGRAPHIC APPARATUS PLANT 3937", US patent No. PCT/GB 2016038 entitled "METHOD PLAYING PLANT PATIC PATIENT 3981, US patent No. PCT/BINET 2016081 entitled" APPLIC PATIC PAT, U.S. patent application No.62/497,781 entitled "APPARATUS FOR HOMOGENING THE OUTPUT FROM A WAVEGUIDE DEVICE", and U.S. patent application No.62/499,423 entitled "WAVEGUIDE DEVICE WITH UNIFORM OUTPUT ILLUMINATION".

Principle of equivalence

The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of this disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.

Claims

1. A waveguide, comprising:

at least one waveguide substrate;

at least one birefringent grating;

at least one birefringence controlling layer;

a light source for outputting light;

an input coupler for directing the light into a total internal reflection path within the waveguide; and

an output coupler for extracting light from the waveguide, wherein interaction of the light with the birefringence control layer and the birefringent grating provides a predefined characteristic of the light extracted from the waveguide.

2. The waveguide of claim 1, wherein the interaction of the light with the birefringence control layer provides at least one of: angle or spectral bandwidth variation; rotating the polarization; a change in birefringence; an angular or spectral dependence of at least one of beam transmission or polarization rotation; and a light transmission variation in at least one direction in the plane of the waveguide substrate.

3. The waveguide of claim 1, wherein the predefined characteristic varies across the waveguide.

4. The waveguide of claim 1, wherein the predefined characteristic is due to a cumulative effect of the interaction of the light with the birefringence control layer and the birefringence grating along at least one light propagation direction within the waveguide.

5. The waveguide of claim 1, wherein the predefined characteristic comprises at least one of: uniform illumination and uniform polarization over the angular range of the light.

6. A waveguide according to claim 1, wherein the birefringence control layer provides compensation for the polarization rotation introduced by the birefringent grating along at least one direction of light propagation within the waveguide.

7. The waveguide of claim 1, wherein the birefringence control layer is a liquid crystal and polymer material system.

8. The waveguide of claim 1, wherein the birefringence control layer is a liquid crystal and polymer system aligned using directional ultraviolet radiation.

9. The waveguide of claim 1, wherein the birefringence control layer is aligned by at least one of: electromagnetic radiation; an electric or magnetic field; a mechanical force; carrying out chemical reaction; and thermal exposure.

10. A waveguide according to claim 1, wherein the birefringence control layer affects the alignment of the LC director in a birefringent grating formed in a liquid crystal and polymer system.

11. The waveguide of claim 1, wherein the birefringence control layer has an anisotropic refractive index.

12. The waveguide of claim 1, wherein the birefringence control layer is formed on at least one of the inner or outer optical surfaces of the waveguide.

13. The waveguide of claim 1, wherein the birefringence control layer comprises at least one stack of refractive index layers disposed on at least one optical surface of the waveguide, wherein at least one of the stack of refractive index layers has an isotropic refractive index and at least one of the stack of refractive index layers has an anisotropic refractive index.

14. The waveguide of claim 1, wherein the birefringence control layer provides a highly reflective layer.

15. The waveguide of claim 1, wherein the birefringence control layer provides optical power.

16. The waveguide of claim 1, wherein the birefringence control layer provides an environmental isolation layer for the waveguide.

17. The waveguide of claim 1, wherein the birefringence control layer has a gradient index structure.

18. A waveguide according to claim 1, wherein the birefringence control layer is formed by stretching a layer of optical material to spatially change its refractive index in the plane of the waveguide substrate.

19. The waveguide of claim 1, wherein the light source provides collimated light in angular space.

20. The waveguide of claim 1, wherein at least one of the input-coupler and the output-coupler comprises a birefringent grating.

21. The waveguide of claim 1, wherein the birefringent grating is recorded in a material system comprising at least one polymer and at least one liquid crystal.

22. The waveguide of claim 1, wherein the at least one birefringent grating comprises at least one birefringent grating for providing at least one of the following functions: beam expansion in a first direction; beam expansion in a second direction and extraction of light from the waveguide; and coupling light from a source into a total internal reflection path in the waveguide.

23. The waveguide of claim 1, wherein the light source comprises a laser and the alignment of the LC directors in the birefringent grating is spatially varied to compensate for the illumination stripe.

24. A method of manufacturing a waveguide, the method comprising:

providing a first transparent substrate;

depositing a layer of grating recording material;

exposing the grating recording material layer to form a grating layer;

forming a birefringence control layer; and

a second transparent substrate is applied.

25. The method of claim 24, wherein:

the grating recording material layer is deposited onto the substrate;

the birefringence control layer is formed on the grating layer; and

the second transparent substrate is applied over the birefringence control layer.

26. The method of claim 24, wherein:

the grating recording material layer is deposited onto the substrate;

the second transparent substrate is applied over the grating layer; and

the birefringence control layer is formed on the second transparent substrate.

27. The method of claim 24, wherein:

the birefringence control layer is formed on the first transparent substrate;

the grating recording material layer is deposited onto the birefringence control layer; and

the second transparent substrate is applied over the grating layer.

28. The method of claim 24, further comprising:

depositing a layer of liquid crystal polymer material; and

aligning a liquid crystal polymer material using oriented UV light, wherein:

the grating recording material layer is deposited onto the substrate; and

the second transparent substrate is applied over the aligned liquid crystal polymer layer.

29. The method of claim 28, wherein the layer of liquid crystal polymer material is deposited onto one of the grating layer or the second transparent substrate.

30. The method of claim 28, wherein:

the layer of liquid crystal polymer material is deposited onto the first transparent substrate;

the layer of grating recording material is deposited onto the aligned liquid crystal polymer material; and

the second transparent substrate is applied over the grating layer.